I receive many questions about lifestyle changes that could beneficially impact intraocular pressure (IOP) and glaucoma. Recently, I've been asked about the potential effects of sauna use, especially infrared saunas, on IOP and glaucoma. Let's dive into this heated issue!
IOP and Glaucoma
First, let's clarify what intraocular pressure (IOP) and glaucoma are. IOP is the fluid pressure inside the eye. Normal IOP ranges from about 12-21 mm Hg, but deviations from this range can occur in healthy individuals without glaucoma. Glaucoma is a group of eye conditions that damage the optic nerve, and elevated intraocular pressure is the most important treatable risk factor. Glaucoma is a leading cause of blindness for people over 60, though it can occur at any age.
IOP and Heat Stress
Back in 2007, a medical hypothesis article piqued my interest in this subject, suggesting that a 20-minute jacuzzi soak could reduce IOP through the action of heat shock protein 70. Here's the link to that brief blog post: Reduce Your Eye Pressure with a Jacuzzi | FitEyes.com (http://www.fiteyes.com/Reduce-Your-Eye-Pressure-with-a-Jacuzzi). Unfortunately, I never proceeded to conduct any actual IOP testing (as I don't have access to a jacuzzi).
In general, heat therapy is increasingly viewed as a novel therapeutic intervention for neurodegenerative diseases, and the most studied mechanism for this beneficial effect is via Heat Shock Proteins.
So let's shift our focus to the closely related topic of Heat Shock Proteins (HSP's) in neuroprotection.
Heat Shock Proteins and Neuroprotection
I'm kicking off the discussion with HSP's and neuroprotection as this is where the bulk of the scientific exploration has been conducted.
Hsp70 is a stress-responsive protein that has been shown to protect the brain from various nervous system injuries (ref). This protein functions as a molecular escort, shielding neurons from protein accumulation and toxicity, safeguarding cells from apoptosis, and defending cells against inflammation (ref).
Hsp70 has been shown to have neuroprotective properties in diseases such as Parkinson's disease, Alzheimer's disease, polyglutamine diseases, and amyotrophic lateral sclerosis (ref).
Hsp27, another HSP family member, has exhibited powerful neuroprotective effects, improving the survival rate of cells exposed to cytotoxic stimuli (ref), (ref). Hsp27 has been shown to protect cells against ischemic insult in cell cultures and can protect neurons against different harmful stimuli such as ischemia and oxidative stress, as well as in neurodegenerative disorders (ref), (ref).
HSP 27 Immunoreactivity Found
I would like to further discuss the results of one study. In this animal study, an increase in Hsp27 immunoreactivity was observed in the nerve fiber layer of elevated intraocular pressure (IOP) eyes, suggesting that glial cells contribute to the increase in Hsp27 seen in experimental glaucoma (ref).
This observation of increased Hsp27 in the nerve fiber layer of the eyes (the part of the eye where retinal ganglion cells send their axons towards the brain) suggests that the cells in this area are undergoing some sort of stress, likely due to the elevated IOP, and are producing Hsp27 as a response to try to protect themselves.
The study also suggests that the increase in Hsp27 observed in this model of experimental glaucoma is contributed by glial cells. Glial cells, often thought of as the "support cells" of the nervous system, are known to react in response to injury or disease in the nervous system. In the context of glaucoma, they may be producing more Hsp27 in an attempt to protect the nerve cells from damage caused by the elevated pressure within the eye. My take-away is that this finding indicates a protective role of Hsp27 in the eyes of rats experiencing elevated IOP, further supporting the evidence I discussed earlier.
Saunas - Background
Now, let's discuss saunas. Traditional saunas heat the air around you and can make your body perspire and heart rate increase. In contrast, infrared saunas utilize infrared lamps to directly warm your body, evoking similar responses at lower temperatures. Both types can induce profound physiological responses, including changes in heart rate, blood pressure, perspiration -- and the production of heat shock proteins.
Sauna Therapy in Other Neurodegenerative Conditions
The 2020 article, "Could Heat Therapy Be an Effective Treatment for Alzheimer's and Parkinson's Diseases? A Narrative Review" by Andrew P. Hunt et al., explores the potential of heat therapy as a novel therapeutic intervention for neurodegenerative diseases, such as Alzheimer's and Parkinson's (ref).
The authors focus on the central role that loss of protein homeostasis plays in the pathophysiology of these diseases, leading to the misfolding and aggregation of proteins. They highlight the importance of HSPs which serve as molecular chaperones, regulating protein aggregation and disaggregation. As we saw above, HSPs, such as HSP70, have been shown to protect against neurodegeneration, making their upregulation a promising therapeutic target (ref). This should apply equally to glaucoma.
Heat therapy and heat acclimation are considered to provide a way to increase HSP expression. In healthy populations, these interventions have been found to increase HSP expression. Besides potential central therapeutic effects, such as reducing the toxicity of protein aggregation, elevated HSPs may also enhance neuromuscular function (ref).
In addition to these effects, heat therapy may also improve muscle function, cerebral blood flow, and metabolic health markers. Such outcomes could be beneficial for those with neurodegenerative diseases such as glaucoma. Several studies have even linked regular passive heating, like sauna bathing, to a reduced risk of developing neurodegenerative diseases. Therefore, the authors call for further research into the potential benefits of heat acclimation and passive heat therapy for neurodegenerative disease sufferers (ref).
Does sauna use affect intraocular pressure?
Coming back to the original question, I did not find many academic publications on this aspect of the question. Here are the only two I found that directly address the question:
Both articles are in German with no English abstracts. They are also very old.
My impression is that the current scientific literature gives us mixed results when it comes to IOP. At least one study suggests that sauna use may temporarily increase IOP, potentially due to increased body temperature or changes in blood pressure and fluid balance. This temporary increase usually normalizes once the body cools down post-sauna. Other studies indicate no significant changes in IOP with sauna use. And then there's that very old source I came across in 2007 that suggested time in the jacuzzi could lower IOP. (I have not tested any of this myself as I currently lack access to a jacuzzi or sauna.)
Is sauna use safe for people with glaucoma?
The science of saunas and their effect on IOP and glaucoma is still evolving. More comprehensive research is needed, particularly concerning infrared saunas.
The overall consensus, given the limited information I found, seems to be that occasional, moderate sauna use does not pose a significant risk for individuals with glaucoma. However, if you are considering sauna use, it would be best to monitor your own IOP with your home tonometer. This is yet another opportunity for us to do self-experiments in an area where the published science is lacking (as it was on the topic of stress and IOP when I started self-tonometry in 2006).